1. Technical Field
The present invention relates to a method and apparatus for rapidly screening and characterizing an array of materials, and more particularly, to an optical device and technique for simultaneously measuring rheological properties of a combinatorial library of materials.
2. Discussion
Combinatorial chemistry generally refers to methods and materials for creating collections of diverse materials or compoundsxe2x80x94commonly known as librariesxe2x80x94and to techniques and instruments for evaluating or screening libraries for desirable properties. Combinatorial chemistry has revolutionized the process of drug discovery, and has enabled researchers to rapidly discover and optimize useful materials such as superconductors, zeolites, magnetic materials, phosphors, catalysts, thermoelectric materials, and high and low dielectric materials.
Analytical techniques that rely on serial measurements of individual library members are often unsuitable for screening combinatorial libraries. Because combinatorial libraries routinely comprise hundreds or thousands of individual library members, viable serial screening techniques require sampling times of a few minutes or less. Although serial techniques can use automation to speed up processing, many sophisticated analytical instruments have relatively long response times, making such instruments impractical for use as screening tools.
Parallel methods represent a useful approach for attaining the requisite sample throughput. Whereas serial screening techniques require instruments having short response times, parallel techniques achieve the necessary sample throughput by measuring one or more properties of all library members simultaneously. Parallel methods can thus use instruments having comparatively sluggish response times. However, the success of any parallel screening method depends strongly on the screening criteria and the information provided by the particular technique.
Optical screening methods possess certain advantages over other techniques because one may adapt existing imaging and image processing technologies for parallel data collection and analysis. Optical characteristics of a compound or material often reveal the electronic properties and spatial arrangement of constituent molecules, making it possible to detect changes in physical or chemical structure through optical measurements. For example, optical measurements have been used to screen for selected characteristics of materials as a function of applied voltage. See, U.S. Pat. No. 6,034,775 and U.S. patent application xe2x80x9cMethod and Apparatus for Screening Combinatorial Libraries for Semi-Conducting Properties,xe2x80x9d Ser. No. 09/414,615, which are herein incorporated by reference.
Thus, there exists a need for other devices and methods for rapidly screening and characterizing, in parallel, optical and physical properties of an array of compounds or materials.
The present invention provides an apparatus for screening an array of at least partially transparent material samples in a combinatorial library, the material samples exhibiting changes in birefringence as a function of environmental conditions. The apparatus includes a sample block having a plurality of regions therein for receiving the library members. The term sample block is not meant to place any structural limitations (e.g. size or shape) on the invention. The apparatus also includes a light source that provides at least one light beam light that is polarized and directed toward the regions, an analyzer for filtering out light having the same polarization as the incident light beam after it passes through the regions, and a detector for analyzing changes in the intensity of the light beams due to the optical characteristics of the library members. The sample block, light source, analyzer and detector are all arranged in series.
Preferably, the sample block receives vials of the material samples within the regions formed therein. The vials that receive the library members can be constructed from any material or combination of materials that are at least partially transparent to the light emitted by the source. Suitable materials include glass, quartz, and transparent plastic sheets, which are generally free of residual stresses. These vials should be nonbirefringent; that is, the vials should not alter the polarization characteristics of light that passes through them.
In accordance with one aspect of the invention, the light source preferably includes a plurality of lights, such as light emitting diodes (LEDs) that are all directed toward the regions simultaneously such that the entire array of material samples may be illuminated at once. A polarizer, such as a commercially available polarizing filter or polarizing mirror, is placed between the light source and the regions to polarize the light before it passes through the vials and material samples in the library. The polarized light beams are then collimated, preferably by passing the light beams through a separate collimator plate, to reduce stray light. As the light passes through the material sample, the sample alters the polarization of the light in a manner determined by the structural characteristics of the material sample. Next, the light beams are passed through a second polarizer or an analyzer, the second polarizer having a preferred polarization direction oriented at 90xc2x0 relative to the first polarizer. The analyzer filters the light beams, only transmitting that fraction of the radiation which has a specific linear polarization.
In accordance with another aspect of the invention, the detector includes a fiber optic assembly and a charged-coupled device (CCD) camera to capture readings of the light intensity transmitted through the material samples. A first fiber optic plate is positioned above the second polarizer and a second fiber optic plate is placed above the first fiber optic plate. A bundle of fiber optics is placed between the plates with the ends of the fibers extending through holes in both plates. Light transmitted through the second polarizer is captured by the fiber ends extending through the first plate, is transmitted through the fibers, emerging at the second plate. The fibers in the bundle are arranged in a tapered configuration so as to reduce the dimensions of the area over which the light is distributed from the array of samples to a size more easily imaged by the CCD camera.
In accordance with another aspect of the invention, the apparatus may also include a temperature-controlled block. The sample block holding the vials of material samples is disposed within the temperature-controlled block such that intensity readings of the material samples may be evaluated as a function of temperature. The apparatus may further include a substantially gas-tight environmental chamber. The sample block holding the vials of material samples is mounted within the substantially gas-tight environmental chamber. At least one gas is directed into the chamber so as to subject the material samples to pressure, wherein intensity readings of the material samples may be evaluated as a function of pressure. Alternatively, the substantially gas-tight environmental chamber may be subject to a continuous mixture of two or more gases so that intensity reading of the material samples may be evaluated as a function of the gas mixture composition.
In accordance with another aspect of the invention, the sample block may further include an array of electrode pairs, wherein a separate electrode pair is associated with each region. The electrode pairs are arranged in an opposing manner, with the region containing the materials disposed there between. A power supply is connected in series with the electrode pairs such that when voltage is applied to the pairs, an electric field is generated across each material sample. The intensity readings of the material samples may then be evaluated as a function of applied voltage.
In accordance with another aspect of the invention, the sample block may further include pairs of electromagnetic devices, wherein a separate electromagnetic device pair is associated with one region. The pairs of electromagnetic devices are arranged in an opposing manner, with the region containing the materials disposed there between. A power supply is connected in series with the pairs of electromagnetic devices such that when voltage is applied, a magnetic field is generated across each material sample. The intensity readings of the material samples may then be evaluated as a function of magnetic field strength.
The present invention also provides a method of characterizing an array of material samples of a combinatorial library comprising providing an array of material samples in transparent sample blocks, e.g. in vials, illuminating at least one material in the array with a beam of polarized light that passes through the vials, filtering out intensity of the polarized light beam that has the same polarization direction as the incident light beam by passing the polarized light beam through an analyzer having a polarization direction oriented at a predetermined angle, (for example and without limitation, 90xc2x0 with respect to the direction of the polarized light beam), detecting changes in the intensity of the polarized light beam due to the optical characteristics of the material sample and determining characteristics of at least one material based on the detected changes in the intensity values. In a preferred method, polarized light beams are arranged such that the entire array of material samples is illuminated simultaneously.
In accordance with another aspect of the invention, the method may further include determining characteristics of the material samples as a function of various environmental conditions. In one embodiment, the temperature of the material samples is varied such that the detecting and determining steps are performed as a function of temperature. In another embodiment the materials are subject to pressure such that the detecting and determining step are performed as a function of pressure. The material sample may also be continuously subjected to a mixture of gases such that the detecting step may be done as a function of gas composition. Further, the method also may include generating an electric field across each material samples such that the detecting and determining step are performed as a function of applied voltage. In yet another embodiment, the method may include generating a magnetic field across each material sample such that the detecting and determining step are performed as a function of magnetic field strength.
The present invention also provides an apparatus for simultaneously measuring rheological properties of an array of material samples. The apparatus comprises transparent, generally planar first and second surfaces that define a substantially uniform gap for containing the material samples. The apparatus includes a device that moves the first surface relative to the second surface so as to exert a shear stress on the material samples disposed within the gap. The apparatus also includes a light source having a first polarization direction and an analyzer having a second polarization direction. The source of light and the analyzer are located on opposite sides of the gap so that light from the source passes through the material samples contained in the gap before striking the analyzer. A detector, which is located adjacent to the analyzer monitors light that passes through the material samples and the analyzer. The detector is capable of distinguishing light transmitted through at least two of the material samples simultaneously. Normally, the first and second polarization directions are orthogonal, so that in the absence of shear the analyzer completely blocks out light from the material samples. When subject to a shear stress, however, the materials may polarize the lightxe2x80x94a phenomenon known as stress-induced birefringencexe2x80x94which appears as a change in the intensity of light exiting the analyzer.
The present invention also provides a method of screening an array of materials based on stress-induced birefringence. The method includes providing an array of materials composed of discrete material elements, which are illuminated with light having a first polarization direction. The method also includes shearing the array of materials by deforming each of the discrete material elements in a direction about normal to the transmission direction of the light, and directing the light from the array of materials through an analyzer having a second polarization direction. Finally, the method includes detecting changes in intensity of the light passing through the analyzer from at least two of the discrete material elements simultaneously. Changes in light intensity are the result of stress-induced birefringence of the materials in the array.